[petsc-users] Why does GPU solve the large sparse matrix equations only a little faster than CPU?

[Matthew Knepley]

On Sat, Aug 4, 2012 at 5:58 AM, Xiangze Zeng <zengshixiangze at 163.com> wrote:

> After I rerun with "deugging=no", the CPU takes 30 minutes, GPU 22
> minutes, a little better than before. The attachment are the output of
> -log_summary.
>

1) Notice how the PCApply takes most of the time, so MatMult is not very
important

2) In g_log_3, notice that every time your PC is called, the vector is
pulled from the GPU to the CPU.
    This means we do not support that PC on the GPU

There is a restriction on PCs since not many are coded for the GPU.
Only PCJACOBI, PCSACUSP, PCSACUSPPOLY, and PCAINVCUSP
work there, see http://www.mcs.anl.gov/petsc/features/gpus.html.

   Matt


> At 2012-08-04 14:40:33,"Azamat Mametjanov" <azamat.mametjanov at gmail.com>
> wrote:
>
> What happens if you try to re-run with "--with-debugging=no"?
>
> On Fri, Aug 3, 2012 at 10:00 PM, Xiangze Zeng <zengshixiangze at 163.com>wrote:
>
>> Dear Matt,
>>
>> My CPU is Intel Xeon E5-2609, GPU is Nvidia GF100 [Quadro 4000].
>> The size of the system is 2522469 x 2522469, and the number non-0
>> elements is 71773925, about 0.000012 of the total.
>> The output of -log_summary is in the attachment. The G_log_summary is the
>> output when using GPU, C_log_summary when using CPU.
>>
>> Zeng Xiangze
>>
>> 在 2012-08-03 22:28:07，"Matthew Knepley" <knepley at gmail.com> 写道：
>>
>>  On Fri, Aug 3, 2012 at 9:18 AM, Xiangze Zeng <zengshixiangze at 163.com>wrote:
>>
>>> Dear all,
>>>
>>> When I use the CPU solve the equations, it takes 78 minutes, when I
>>> change to use GPU, it uses 64 minutes, only 15 minutes faster. I see some
>>> paper say when using PETCs with GPU to solve the large sparse matrix
>>> equations, it can be several times faster? What's the matter?
>>>
>>
>> For all performance questions, we at least need the output of
>> -log_summary. However, we would also need to know
>>
>>   - The size and sparsity of your system
>>
>>   - The CPU and GPU you used (saying anything without knowing this is
>> impossible)
>>
>>    Matt
>>
>>
>>> Thank you!
>>>
>>> Sincerely,
>>> Zeng Xiangze
>>>
>>>
>>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>>
>>
>>
>
>
> --
> Mailbox 379, School of Physics
> Shandong University
> 27 South Shanda Road, Jinan, Shandong, P.R.China, 250100
>
>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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